Various types of infinitely variable transmissions use an arrangement in which one of the transmission elements has a plane flat surface extending essentially at right angles to the drive shaft, and another one of the surfaces is essentially cone shaped. Actually, the surface is slightly curved, but in general approximates that of a shallow cone. The referenced patents, and specifically U.S. Pat. No. 4,276,041, illustrate such an arrangement. In such a transmission a chain with engagement elements is located between two pairs of friction disks, each located on an individual shaft. One of them is the drive shaft and the other a driven shaft. The chain runs between the wedge-shaped zone defined by the flanks of the respective friction disks. The chain is a link chain with linked elements which have transversely extending pressure or engagement elements. The pressure or engagement elements transmit frictional force between the disks and the engagement elements. The center points of the somewhat bowed engagement surfaces, radially, are on or beyond the contact positions of a theoretical parallel line to the respective operating axis of the disk pair.
Cone disk transmissions with asymmetrical reception region for the drive chain are frequently used where a compact construction is desirable. A single drive chain can be used to connect two such cone disks, or a dual transmission can be used, which can transmit high power within small space. In a dual system, a central disk having two essentially plane or flat faces is positioned between two cone disks. In a single chain transmission, the cone disk is axially shiftable on its shaft to adjust the transmission ratio; in a dual chain arrangement, at least one of the cone disks can be axially shiftable and, additionally, the central disk with the two essentially flat surfaces can shift axially. Of course, it rotates with the respective shaft, and is splined, or otherwise connected thereto to rotate therewith.
The transmission ratio of the overall system is changed by making diametrically oppositely positioned friction disks of the respective pairs on the respective shafts to be axially shiftable; the other friction disks, all having the conical surface, are axially secured to the respective shaft. The distribution between the axially fixed and axially shiftable friction disks, as described, maintains an essentially right angle running direction of the connecting chain with respect to the drive shafts, and effectively eliminates an axial offset, or change in tracking of the connecting chain. The connecting chains, with the engagement elements, can tolerate an offset in their longitudinal or running direction only to a very limited extent. To further improve the longitudinal running direction of the respective runs of the connecting chain, the conical surfaces are not strictly cone surfaces but, rather, are slightly bowed or bulged, in which the bowing follows a mathematical curve so designed that, within the adjustment range or transmission ratio, practically no change in the direction of the runs of the chain will obtain.
The friction disks with the flat faces provide engagement surfaces which are not precisely perpendicular to the running shaft. Exact radial alignment of these engagement flanks is not possible since, otherwise, the run-on of the chain in the wedge-shaped engagement zone would be undesirably influenced. Rather, the flanks have a slight clearance inclination, that is, define a cone with a cone angle of about 89.degree., to provide a 1.degree. clearance towards the outer open region of the wedge-shaped engagement zone. This results in a slight tracking offset for the operating chain, which, however, is so small that it is acceptable. Additional increase of the axial offset of running of the chain due to changing the bowing of the conical friction surfaces should be avoided, however, since danger of contacting of the edge of the almost planar surface of the flat running chain might otherwise occur.
Various types of connecting chains for infinitely variable transmissions are known, and different arrangements may be used. The referenced U.S. patents show such chains. For example, U.S. Pat. No. 3,089,346 describes a chain in which the pressure elements are located either between the link positions of a link package or the pivot elements of the chain simultaneously form the pressure elements. Similar constructions are also shown in U.S. Pat. Nos. 3,364,767 3,353,421 and 3,916,709.
The connecting chains of the prior art have essentially circularly bent or bowed engagement surfaces. The bowing or bending on both sides of the pressure elements is the same. The entrance plug element and the exit plug elements, retained within the sleeve, preferably are infinitely variable cone transmissions having asymmetrical engagement region, that is, in which two cone surfaces face each other do not introduce further problems. In variable transmissions, however, having an asymmetrical engagement wedge zone requires further consideration for the formation of the engagement surfaces of the engagement elements, so that no tipping torque or tipping moment is caused by the asymmetry of the engagement wedge zone which can be transmitted to the pressure elements and hence to the chain itself. Such torques or moments would, otherwise, tend to twist the chain in the running direction, resulting in highly variable and differing longitudinal loading of the chain with respect to its width. The requirement of freedom from a tipping or twisting torque can be fulfilled by suitably shaping the facing surfaces, that is, by suitably shaping the bowing of the surfaces so that the resulting force which is applied to the pressure element goes through a common point which is located in the center of the pressure element, considered transversely to the running direction of the chain. As a result of such considerations, the bending radius of the engagement surfaces of the pressure elements, in all chains for an asymmetrical engagement zone, corresponds to half the thickness of the pressure elements, measured transversely to the running direction of the chain. This leads to a comparatively highly bowed or curved engagement surface. Such a highly curved surface results in high specific engagement pressure at the contact points between the engagement elements add the friction disks. High performance transmissions, with high transmission torques, may then have the tendency to form grooves on the friction disks, and subject the chain contact points to high wear. The operation time and the operating reliability of the transmission is determined in part by the generation of heat, and its dissipation, due to friction. Additionally, wear and tear and fatigue of material must be considered, so that the overall efficiency and efficacy of power transmission of the apparatus may be limited. The formation of grooves likewise increases the surface contact between the disks and the engagement element, which leads to hydrodynamic slippage with the well-known negative results that consistency of frictional engagement of the pair of pressure element - friction disk is no longer assured.